Electrode for electroplating planar structures

ABSTRACT

An electrode apparatus for electroplating a metal overlay on a substrate having a front surface, a back surface, and a seed layer deposited on all surfaces. The apparatus includes a cell for containing and circulating an electrolyte; an annular sealing fixture having a “J” shaped cross section for supporting the peripheral front surface of the substrate. The substrate is supported above the cell by the shorter and inner member of the “J” shape. A multiplicity of compliant electrode fingers are inwardly mounted with a downward tilt angle, the compliant fingers are equally spaced about the inner periphery of the longer “J” member. The compliant fingers make conductive cathodic contact with the seed layer at the peripheral edge of the substrate. A pressure is applied to the back surface of the substrate. The pressure effects a wiping action between the compliant fingers and the peripheral edge while holding the substrate against the sealing fixture. A counter electrode is proximally placed towards the bottom of the cell and is circuitous arranged for passing current between the counter electrode and compliant electrode fingers. A pump circulates the electrolyte against the front surface of the. substrate.

BACKGROUND OF THE INVENTION

(1) Technical Field

This invention relates to the field of semiconductor processing, andmore particularly, to an electrode contact structure used for connectingto a substrate or wafer during electroplating

(2) Description of the Prior Art

The uniformity of depositing a metal layer onto wafer surfaces byelectroplating is directly related to the contact resistance between athin metal seed layer previously sputtered, and a cathode electrode.

In recent years, escalating requirements for high density and highperformance have created the need for improved thickness uniformity.

There are considerable difficulties in the electroplating process in thecontext of a semiconductor substrate, including undesirableelectroplating on the contact fingers, thereby generating contaminatingparticles, and unwanted electro-deposition of metal on the backside andedges of the substrate.

The following documents relate to various electroplating tools andprocesses.

U.S. Pat. No. 5,833,820 issued Nov. 10, 1998 to Valery Dubin discloses atilt angle contact to a wafer in a plating tool.

U.S. Pat. No. 6,132,587 issued to Jome at al.; U.S. Pat. No. 6,108,172issued to Hagen; U.S. Pat. No. 6,077,412 issued to Ting et al; and U.S.Pat. No. 4,389,296 issued to Seyffert et al., show various plating toolsand processes.

BACKGROUND OF THE RELATED ART

The present invention is concerned with conformal contact with asubstrate to tolerate dimension variation of the plated substrate.

In the manufacture of devices on a semiconductor wafer, it is now thepractice to fabricate multiple levels of conductive (typically metal)layers above a substrate. The multiple metallization layers are employedin order to accommodate higher densities as device dimensions shrinkwell below one micron design rules. The size of interconnect structureswill shrink correspondingly in order to accommodate the overall smallerdimensions. Thus, as integrated circuit technology advances into thesub-0.25 micron range, more advanced metallization techniques are neededto provide improvements over existing practices.

In order to fabricate features, circuits and devices on a substrate,such as a semiconductor wafer, various techniques are used to depositand etch materials on the wafer. Deposition techniques include processessuch as PVD, CVD, sputtering and immersion of the wafer in anelectrolyte. The last technique can be used for either electrolessdeposition or electroplating.

In an electroplating technique, applicable to the current invention, thecells are tanks with sides and a bottom with a drain port on the bottomsurface and an opening at the top which permits the substrate to befully immersed in the electrolytic solution. The cell also includes asealable top, or lid, per se, to hold the wafer in place and contain theelectrolytic solution during immersion and/or inversion, minimizingleakage of the solution during the electroplating process. Once thesubstrate is immersed in an electrolyte, it is positioned in an electricfield between a cathode and an anode, in which charged particles aredeposited onto the surface of the substrate or wafer.

The present invention addresses the electroplating technique, in which amaterial is deposited on a substrate. The technique is implemented witha novel, contact electrode with a tilt angle permitting the describedtechnique to be employed for the mass production of semiconductorproducts while eliminating some of the major manufacturing problemsinherent in the process.

The current electroplating structures are limited by large area penaltyand considerable backside and edge contamination problems.

There are many difficulties in the electroplating process in the contextof a semiconductor substrate. Specifically, during electroplating,metallic fingers are used to provide electrical contact with a seedlayer on a substrate. During the electroplating, metal from theelectroplating solution is electroplated on the contact fingers,generating contaminating particles when the electroplated metal isdelaminated from the contact fingers. In addition, electroplated metalon the contact fingers leads to increased contact resistance and canresult in a high voltage drop and failure.

Another problem frequently encountered electroplating a metal on asubstrate is the undesirable electro-deposition of metal on the backsideand on the edges of the substrate.

SUMMARY OF THE INVENTION

This invention describes a device for a contact electrode with a tiltangle edge to tolerate dimension variations in the plated material.

An object of the tilt angle edged contact electrode structure is toallow for less area penalty when electroplating a metal on a substrate.

Another object of the invention is to offer a method to prevent metalplating on contacts during electroplating thereby reducing particulatecontamination and improving thickness uniformity, and thus, performance.

Yet another object of the invention is the reduction in the possibilityof backside and edge contamination during the process of plating metalon the front side of a substrate by preventing electro-deposition ofmetal on the backside and edges of the substrate.

Still another object of the invention is to provide for personalizationof the electroplating process, thereby expanding both the limits and thecustomization capabilities of the electroplating process for manyapplications that current devices cannot accommodate.

When used in conjunction with photo resist, the invention expands thelimits of the electroplating process and allows for personalization ofthe process for applications with special needs or inherentdifficulties. A typical process includes:

(1) coating the substrate with a photo resist to limit or to personalizethe electroplating.

(2) drying the photo resist.

(3) spray rinsing the edge of the wafer, with a photo resist solvent, toremove resist from the edge area, thereby, establishing a contactsurface for the electrode.

(4) exposing and developing the photo resist for electroplating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the prior art showing the currentpractice of a face down electroplating cell.

FIG. 2 is a schematic drawing of the prior art showing the currentpractice of a face up electroplating cell.

FIG. 3 is a is a schematic drawing of the prior art showing the currentpractice of a horizontal electroplating cell.

FIG. 4 is a schematic drawing of the preferred embodiment showing thepractice of a face down electroplating cell.

FIG. 5 is a schematic drawing of the preferred embodiment showing thepractice of a face up electroplating cell.

FIG. 6 is a schematic drawing of the preferred embodiment showing thepractice of a horizontal electroplating cell.

FIG. 7 is an illustration of the invention showing the contact pointsaround the periphery of the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is designed to provide a new, tilt angle edge contactelectrode structure for electroplating a metal on a substrate comprisinga back side and a front side with a seed layer deposited on the frontside.

The preferred embodiment's tilt angle edged contact electrode structureallows for less area penalty when electroplating a metal on a substrate.

The invention also offers a method to prevent metal plating on contactsduring electroplating thereby reducing particulate contamination andimproving thickness uniformity, and thus, performance.

And, the invention reduces the possibility of backside and edgecontamination during the process of plating metal on the front side of asubstrate by preventing electrodeposition of metal on the backside andedges of the substrate.

Importantly, the invention provides for personalization of theelectroplating process, thereby expanding both the limits and thecustomization capabilities of the electroplating process for manyapplications that current devices cannot accommodate, e.g., for a postpassivation process or redistribution metal process such as using Au orCu on different wafer sizes.

Accordingly, an electrode apparatus for electroplating a metal overlayon a substrate having a front surface, a back surface, and a seed layerdeposited on all surfaces. The apparatus includes a cell for containingand circulating an electrolyte; an annular sealing fixture having a “J”shaped cross section for supporting the peripheral front surface of thesubstrate. The substrate is supported above the cell by the shorter andinner member of the “J” shape. A multiplicity of compliant electrodefingers are inwardly mounted with a downward tilt angle, the compliantfingers are equally spaced about the inner periphery of the longer “J”member. The compliant fingers make conductive cathodic contact with theseed layer at the peripheral edge of the substrate. A pressure isapplied to the back surface of the substrate. The pressure effects awiping action between the compliant fingers and the peripheral edgewhile holding the substrate against the sealing fixture. A counterelectrode is proximally placed towards the bottom of the cell and iscircuitous arranged for passing current between the counter electrodeand compliant electrode fingers. A pump circulates the electrolyteagainst the front surface of the substrate.

FIGS. 1 and 2 are schematic drawings of the electroplating cells,illustrating the current practices for face down and face upelectroplating respectively. The face down electroplating cell 15 shownin FIG. 1, is a tank with sides and a bottom with a fill port on thebottom surface and an opening at the top which permits the front surfaceof a substrate to be exposed to the electrolytic solution. The cell alsoincludes a sealable fixture 13, for supporting the substrate and forminimizing leakage of the solution during the electroplating process.The front surface of the substrate 10 is exposed to the electrolyte 14and positioned in an electric field between a cathode 20 and an anode16, in which charged particles are deposited onto the surface of thesubstrate 10. The sealing fixture 13 holds the substrate in place.

FIG. 3 illustrates the same process of the current practice for avertical electroplating cell where the substrate is placed with itsfront surface against the sealing fixture, the fixture is placedvertically into the electrolyte and positioned in an electric fieldbetween a cathode 20 and an anode 16, in which charged particles aredeposited onto the surface of the substrate 10.

FIGS. 4 and 5 are schematic drawings of an electroplating cell forselectively electroplating materials onto a metalized substrate 10 whenthe metalized substrate is subjected to an electrolytic solution 14 andan electric field.

Referring to FIGS. 4 and 5 showing schematic drawings of the preferredembodiment for a face down and face up electroplating respectively. FIG.4 illustrates a face down electroplating cell 15, embodying sides and abottom with a fill port 23 on the bottom surface and an opening at thetop which permits the front surface of a substrate to be fully exposedto an electrolytic solution 14. The cell also includes an annularsealing fixture 13 mounted on top which supports and seals the frontsurface of an object or substrate, per se, held in place by a pressurefixture 24, which is urged against the back surface, which serves tohold the substrate in place and contain the electrolytic solution duringimmersion, minimizing egress of the solution during the electroplatingprocess. FIGS. 4 and 5 showing the substrate 10 in the electrolyte cell15 with electrolyte 14 and illustrates electrode fingers 11, each with atilt angle for making wiping contact between the first end of a contactfinger and the peripheral edge of the substrate which has a conductiveseed layer previously applied to all surfaces of the substrate. Thematerial of the electrode fingers 22 is a compliant yielding metal andmay take the form, for example, of a titanium metal finger having a PTcoating, or, alternatively, this finger may be a simple titanium wire.

The contact electrode includes a plurality of spring-loaded contacts 22,so contact is made at multiple sites and pressure holds the substrate 10in place. The electrical contact resistance is reduced because of thewiping action between the seed layer at the edge of the substrate andthe compliant electrode fingers.

FIG. 6 deals with the same process of the preferred embodiment for ahorizontal electroplating cell.

FIG. 7 shows the front face of the substrate 10 to illustrate thecontact of a multiplicity of complaint electrode fingers 19 with theexposed seed layer 25 around the periphery of the substrate 10 and photoresist 26 masking the personalized area not to be electroplated.

Reiterating the description of the electrode apparatus used primarilyfor electroplating a metal overlay on a substrate 10 having a frontsurface, a back surface, and a seed layer deposited on all surfaces. Theapparatus includes a cell 15 for containing and circulating anelectrolyte 14, an annular sealing fixture 13 having a “J” shaped crosssection for supporting the peripheral front surface of the substrate.The substrate 10 is supported above the cell 15 by the shorter and innermember of the “J” shaped sealing fixture 13. A multiplicity of compliantelectrode fingers 22 are inwardly mounted with a downward tilt angle,the compliant fingers 22 are equally spaced about the inner periphery ofthe longer “J” member. The compliant fingers make conductive cathodiccontact with the seed layer at the peripheral edge of the substrate 10.A pressure is applied to the back surface of the substrate. The pressureeffects a wiping action between the compliant fingers and the peripheraledge while holding the substrate 10 against the sealing fixture 13. Acounter electrode 16 is proximally placed towards the bottom of the cell15 and is circuitous arranged for passing current between the counterelectrode 16 and compliant electrode fingers 22. A pump (not shown)circulates the electrolyte against the front surface of the substrate.

While the invention has been particularly shown and described withreference to the preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and details may be madewithout departing from the spirit and scope of the inventions.

What is claimed is:
 1. A method for selectively exteriorizing anelectroplated metal on a substrate, comprising the steps of: providingan electroplating structure having; a cell means for containing anelectrolyte; a sealing fixture adapted to support a substrate above saidcell means, said sealing fixture supports an annular outlying area of afront surface of said substrate, said sealing fixture includes aplurality of complying electrode members affixed with a tilt angle, eachof which makes electrical contact with a portion of a peripheral edge ofsaid substrate; said substrate is urged and held against said sealingfixture forcing said substrate against a plurality of complyingelectrode members, and a counter electrode placed distally in said cellmeans; means arranged for passing current between said counter electrodeand said complying electrode members; a pump means for forcingelectrolyte against said front surface of said substrate.
 2. The methodaccording to claim 1 and further comprising the steps of: providing asubstrate with integrated devices formed therein; sputter a metal seedlayer over entire surface of said substrate for personalizing andelectroplating contact; applying a photo resist on the operative side ofsaid substrate; remove photo resist from peripheral edge area of saidsubstrate that will be contacted by said complying electrode members;expose and develop said photo resist to limit or to personalize saidelectroplating.
 3. The method according to claim 1 wherein saidplurality of compliant fingers are made of a flexible conductive metal.4. The method according to claim 1 wherein the downward tilt anglerenders a gentle pressure component and a wiping action to saidperipheral edge area of said substrate to reduce any contact resistancebetween said compliant fingers and said seed layer.
 5. The methodaccording to claim 1 wherein said tilt angle of said compliant fingersendures dimensional variation of plated layers.
 6. The method accordingto claim 1 wherein said electrode apparatus reduces plating defectsassociated with a large area substrate.